In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium, to form characters and images. The ink-jet printing methods have been rapidly spread because of their various advantages such as easiness of full coloration, low costs, capability of using ordinary paper as the recording medium, non-contact with printed images and characters, etc. Among such printing methods, in view of enhancing the weather resistance and water resistance of printed images and characters, an ink-jet printing method utilizing an ink containing a pigment as the colorant has now come to dominate (for example, refer to JP 10-338826A, JP 2000-336292A and JP 2001-329199A).
JP 10-338826A discloses an ink containing a solubilized resin emulsion that is produced by polymerizing a mixture containing water, a surfactant and an olefinic monomer such as acids thereof, a vehicle and a colorant in order to improve image-staining characteristics of the ink.
JP 2000-336292A discloses a pigment-dispersed ink-jet printing ink containing an acrylic emulsion produced from a monomer mixture containing 10 to 70% by weight of acrylic monomer having a polyoxyalkylene constitutional unit, and a pigment for the purpose of improving an ejection stability, an image sharpness, etc.
Also, JP 2001-329199A discloses an ink composition containing polymer particles containing a polyalkoxyalkylene derivative, etc., and a self-dispersible pigment to improve a high lighter-fastness and a rubbing resistance thereof.